One of the most striking things about the American pop scene is just how un-American it’s become. Kanye West’s recent televised tirade against George W. Bush notwithstanding, the un-Americanism at hand isn’t political, but literal: Many chart-topping artists today simply aren’t American-born. Barbados-bred club sensation Rihanna — whose ubiquitous smash “Pon De Replay” is one of the simplest, most effective hits in recent memory — is a case in point. But if her debut album is any indication, she’s going to have a tough time staying relevant in today’s throwaway pop world. Though her sunny, Caribbean-informed beats and Beyonce-lite have their appeal, she ultimately proves to be more like a little Florida orange than an exotic tropical fruit. (Her juice just isn’t that sweet.)

Most of the strength of “Music of the Sun” lies in its inventive rhythms. Though there’s nothing here that approaches the glimmering heights of the Neptunes or Timbaland, Rihanna’s producers skillfully fuse gritty reggae overtones with an easily approachable urban sensibility. On “You Don’t Love Me (No, No, No),” Rihanna and her collaborator, Jamaican MC Vybz Kartel, bounce banter over bass-thumping scratching and a dynamic ska-like beat. Rihanna’s twangy vibrato and catchy melodies spice up the beach-party track, though it’s hard to imagine enjoying the song in any other setting.

There are much more weighty results when she briefly indulges her hip-hop side (she is, after all, Jay-Z’s first big signing as a music executive.) On “Let Me,” steel drums provide an exotic beat for Rihanna’s rapid-fire singing. Better still, the warehouse-style bass thwacks on “That La La La” are positively ear-splitting, while breathy whispers and twirling electronic whistles juxtapose a dark dancehall vibe against a glow-stick-lit rave scene. Rihanna’s inner Aaliyah takes charge. She supplements her ample vocal range with some of the sex appeal that had been missing since track 1, deftly snapping the “La la la” refrain against an industrial-strength beat.

Aaliyah is the most prominent of Rihanna’s R&B influences. “The Last Time,” with its humble acoustic instruments and dense, restrained bassline, is a fitting shadow for Aaliyah’s monumental “I Care 4 U” (produced by Timbaland, of course). Few can match the late diva, but the emoting teenager doesn’t do badly.

The squeaky-clean image Rihanna maintains throughout most of the album subdues the blistering hotness she so scrupulously embodies on “Pon De Replay,” the album’s opening track. (In all likelihood, it will be the biggest hit of her career — though to be fair, one of the biggest of the year as well.) On “Replay,” her lilting voice hides an edginess that she subtly wraps around the fluid, propulsive beat. When she reaches the now oft-repeated refrain of “Please mister DJ/ Tell me if you hear me/ Turn the music up,” you genuinely feel her longing. But on songs like “You Don’t Love Me” and “Here I Go Again,” that sense of naughtiness is replaced by adolescent angst — granted, the artist isn’t even 18 yet, but in this context, “Pon De Replay” is little more than an empty tease.

But then there is pure drivel like “Now I Know,” a bloated, belabored number that closes out the album. The only thing worse than the off-tempo piano and Bat Mitzvah-party lyrics (“Like a dance/ Started slow/ And then love took control”) are the practically laughable Diane Warren violin flourishes.

Rihanna would have been better served to stick it out with an album chock-full of up-tempo “Replay” rip-offs than to dive into this syrup-ballad territory. (As a matter of fact, the spunky remix of “Replay” at the end of the CD is a bona fide highlight). Other offenders include the listless title track, the awkwardly prissy “Willing to Wait” and the decidedly un-thug “There’s a Thug In My Life.”

“There’s a thug in my life/ How am I gonna tell my mama?” Rihanna asks, with an excruciating lack of irony. “She’s gonna say it ain’t right/ But he’s so good to me.”

But for every “Thug” and “Now I Know,” Rihanna manages to make some surprising, delightful pop music. If only the other half of her album didn’t aim right for middle America.